The present invention relates to the field of photolithographic techniques. More specifically, one embodiment of the invention provides an improved lithographic method that is optimized for fabricating Thin Film Heads (TFH), Charge Coupled Devices (CCD), moderate resolution semiconductors, and any other electronic circuit or images whose smallest field dimension can be practically relayed by a lens system and whose second dimension may be significantly larger than the lens system. Still more specifically, the present invention relates to a manufacturing method and apparatus wherein an image from a photomask or a reticle (hereafter called a reticle) is imaged onto a photosensitive substrate by multiple passes of one dimensional scanning means.
Currently, there are three types of machines used for printing micron size images on moderate to large substrates in the manufacture of electronic devices like flat panel displays, semiconductors, and multi-chip modules. The first type of machine is called a contact or proximity printer. This is the oldest type of machine. In a contact printer, the reticle and substrate are in contact or close proximity and are aligned to each other. A flood exposure illuminator illuminates the reticle and thereby exposes the substrate. This machine is relatively low in cost, but has the large disadvantage that reticles are ruined after a certain number of uses, and its use induces frequent defects in the product. Manufacturers who use these machines would like to switch to one of the other two types of machines, except the cost is often prohibitive.
A second type of machine is commonly called a step-and-repeat camera because it moves to a specified location and prints a portion of the photosensitive substrate and then moves to another location and typically prints the same image on that portion of the substrate, repeating the process until the entire substrate is printed. Steppers were developed for integrated circuit fabrication where high resolution features within small repetitive patterns typify the product. Various object to image magnifications are used by different equipment manufacturers. When a stepper is used to expose a pattern larger than its field size onto a substrate, multiple images must be stitched together with high precision to create the desired large product. One major disadvantage of the step-and-repeat technology is the need for very precise alignment to seamlessly stitch adjacent fields together, and a very complex stage with a precise metrology system.
A third type of machine is called a scanner. The largest format scanners print six inch (150 mm) wide image at 1.times. magnification with resolutions down to about 1 micrometer. The scan is a single axis smooth motion of a substrate under a lens system. The scan can be any length, but the illuminated width is limited to the lens field. The optics are usually designed to cover the width of the substrate. Similarly, the reticle dimensions are slightly greater than the substrate. Hybrid scanners have been built that print two six inch wide images that are aligned adjacent to each other like steppers do.
The steppers and scanners, particularly those made for moderate to large substrate lithography, are complex, expensive, and very large, consuming area of expensive clean room floor space due to their large substrate stages. The stage blind stepping performance requires high precision alignment as well as complex and expensive metrology.
From the above information it is seen that an improved system and method for printing moderate resolution images on moderate to large substrates is needed.